The present invention relates to a transport system and particularly to a transport system capable of conveying articles in a fabrication system.
FIG. 1 is a schematic view showing a conventional fabrication system layout. A fabrication system 100 capable of fabricating semiconductor wafers comprises tool bays 130A and 130B, stockers 120A and 130B, and a plurality of transport systems 110, 115A, and 115B.
Each tool bay 130A and 130B comprises a plurality of processing tools. These tool bays comprise, in general, a number of processing tools for performing various wafer fabrication functions.
Stockers 120A and 120B serve tool bays 130A and 130B respectively. These stockers store carriers loaded with wafers before and after processing.
Each transport system uses carriers for storing and transporting wafers. Within the fabrication system 100, an interbay transport system 110 transfers carriers from one tool bay to another; intrabay transport systems 115A and 115B transport carriers within tool bays 130A and 130B, respectively.
The interbay transport system 110 provides an uninterrupted high throughput material movement across long distances using an overhead shuttle (OHS). The OHS is a high-speed transport mechanism suitable for long distance cross-bay transport.
The intrabay transport systems 115A and 115B use an overhead hoist transport (OHT) for transport, which is suitable for short distance intrabay transport.
The interbay and intrabay transport systems are physically incompatible. The carriers adapted for use in the interbay transport system cannot be used in the intrabay transport system, or vice versa.
Because of the incompatibility, wafers are transferred between different carriers at the stockers when transported between the interbay and intrabay transport systems.
Taking FIG. 1 as a reference, a plurality of semiconductor wafers are scheduled to transport from a processing tool 101 in the tool bay 130A to a processing tool 103 in the tool bay 103B. First, the wafers are loaded into a carrier A through a load port 1101 of the processing tool 101, wherein the carrier A is adapted for use in the intrabay transport system 115A. The carrier A is transported to the stocker 120A through the intrabay transport system 115A. Then the carrier A is handed off from the intrabay transport system to the stocker 120A. The wafers transported are removed from the carrier A and loaded into a carrier I, which is adapted for use in the interbay transport system. The carrier I is transported to the stocker 120B through the interbay transport system 110 and handed off to the stocker 120B. Then the wafers transported are removed from the carrier I and loaded into a carrier B, which is adapted for use in the intrabay transport system 115B. The carrier B is transported to its targeted processing tool 103 through a load port 1031.
Such conventional transport systems have several disadvantages.
First, the conventional transport system is not efficient for short distance cross-bay transport. When wafers are transported between processing tools located in two adjacent tool bays, most of the transport time is spent, not in actual transport, but rather in transfer operations due to the system incompatibility mentioned above.
In addition, the interbay transport system conveys articles in a predetermined direction, for example, clockwise, as shown in FIG. 1 by an arrow D1. Articles must travel nearly completely around interbay transport system 110, when they are transported from the tool bay 130A to the tool bay 130B, even though the bays are adjacently located.
Second, the stockers and interbay transport system become traffic bottlenecks of the conventional transport system. Generally, there is only one crane in a stocker and one or two interbay transport systems in a semiconductor fabrication system. Thus the interbay transport system and stockers may be overloaded and cause traffic congestion in times of heavy traffic.
Third, a malfunction of the interbay transport system has a great impact on the fabrication system. The interbay transport system is the backbone of the transport system and serves as the sole mechanism to convey articles between the tool bays. When the interbay transport system fails, every tool bay is isolated, there is no way to feed wafers to any tool bay or remove wafers from any tool bay other than by manual transfer.
Hence, there is a need for a transport system that addresses the incompatibility problems arising from the existing technology.